The objective of the study is to obtain data on association and linkage between schizophrenia and 25 genetic markers using as material 50 sibships containing at least three individuals, one of whom has been diagnosed as schizophrenic on the basis of research criteria. At the same time, an HL-A association study will be conducted using 10 HL-A antigens. The material consists of schizophrenic sibships which have already been located and interviewed as part of an ongoing research project. This project will entail recontacting the subjects, reinterviewing those about whom there is some diagnostic ambiguity, and drawing blood samples for the above analyses. This work will be conducted by a properly trained registered nurse. Based on a preliminary analysis of the data, we estimate a minimum of 200 individuals in the overall sample, whom we plan to gather data on over a two-year period. The data will be analyzed for genetic linkage and association between schizophrenia and the 25 marker loci, and the HL-A antigens will similarly be analyzed for association. HL-A typing will be performed on 100 subjects, 50 schizophrenics and 50 sibling controls. We will also carry out the analyses on paranoid and non-paranoid subtypes, as well as diagnoses of schizophrenia spectrum versus nonspectrum. A finding of association would provide additional evidence in support of a genetic predisposition to schizophrenia. A positive linkage finding would implicate a major gene in the etiology of schizophrenia as opposed to a polygenic model. A positive HL-A association would represent suggestive evidence for an infectious etiology.